Multiple stage hydraulic fluid systems have been known and practiced in various of the arts for a long time. Such type systems provide variable outputs from a single mechanism and a primary application for such systems pertains to the injection molding art. In the injection molding process it is desirous to provide a fast-action closure of a mold and then to maintain the mold closure under a high pressure force during the injection molding cycle. Such systems are found and disclosed in U.S. Pat. Nos. 4,443,179 to Wohlrab and 4,861,259 to Takada.
Other applications for multiple stage actuation involve material handling machines which require dual speed lifting arms as disclosed in U.S. Pat. No. 3,186,309 to Killebrew and to various type presses requiring reciprocating action as disclosed in U.S. Pat. No. 3,602,098 to Balkee.
Further, these type multiple stare systems have been applied to various brake applications as exemplified in U.S. Pat. Nos. 4,496,033 to Hall et al and 2,820347 to Highland et al. The Highland et al mechanism is configured to change the hydraulic fluid pressure from an initial low pressure to a final high pressure such as to effect operation of a brake device.
The present invention may be applied to many and various applications including those mentioned above and it is in accordance with a primary aspect thereof to provide a hydraulic fluid actuator which accomplishes a fast forward output stroke followed by a high pressure output force such as to maintain position of the output during a particular machine operation while pumping and returning a relatively low volume of hydraulic fluid.
In accordance with another aspect of the present invention it is an object to provide a hydraulic fluid-operated actuator which is dual speed and double acting such as to increase the number of actuator cycles in a particular period of time.
According to still another aspect of the present invention it is an object to provide a hydraulic actuator which is simple in design and easily controlled and which may be operated in various mounting configurations to accomplish an initial fast forward output stroke followed by a greatly increased output force.
According to another aspect of the present invention it is an object to provide an actuator which may be operated using various arrangements of hydraulic fluid pumps, valves, and reservoirs to accomplish an initial fast forward output stroke followed by a high pressure output force and then a fast reverse stroke to complete an actuator operation cycle in the shortest period of time while pumping and returning a minimum volume of hydraulic fluid.